APPLICATIONS OF RADIATION IN MEDICINE. Kirstin Murray BSc (Hons) Radiotherapy & Oncology

Transcription

1 APPLICATIONS OF RADIATION IN MEDICINE Kirstin Murray BSc (Hons) Radiotherapy & Oncology

2 CONTENTS Principles of Radiation Therapy Radiobiology Radiotherapy Treatment Modalities Special Techniques Nuclear Medicine

3 X-RAYS 1895 Professor Wilhelm Conrad Roentgen discovered x-rays by accident Experimented with x-rays using vacuum tubes and saw the could pass through wood, paper, skin etc. Took 1 st x-ray of his wife s hand using photographic plate 1896 Henri Becquerel discovered radioactivity 1898 Marie Curie discovered radium X-rays widely used as essential diagnostic tool in medicine, but also in cancer treatment

4 WHAT IS CANCER? Cancer describes disease characterised by uncontrolled and unregulated cell division that invades healthy tissues and affect their function Cancer can be malignant or benign (do not spread to distant parts) Malignant cells can spread locally or to distant parts of the body via the bloodstream or lymphatic system Treated with surgery, chemotherapy, radiotherapy, hormone treatments (conventional medicine)or in combination e.g.. Pre or post surgery

5 PRINCIPLES OF RADIOTHERAPY Deliver maximum radiation dose to tumour to achieve cell death whilst minimising dose to neighbouring healthy tissues Approximately 50% cancer patients treated with radiotherapy Royal College of Radiologists estimates that 40% of all long term cancer survivors owe their cure to radiotherapy High doses of radiation needed for tumour control Sensitivity of tumour vs. sensitivity of normal tissue= Therapeutic Ratio

6 Oncologist will prescribe a dose to the tumour volume (Gray) 1 Gy = 1J/kg PRINCIPLES OF RADIOTHERAPY Named after the British physicist Louis Harold Gray Treatment is delivered in sessions or fractions The time over which the dose is delivered is very important Patients may attend treatment for 1 day to up to 7 weeks, depending on the Intent of the treatment Radiotherapy given radically (cure) or palliative (symptom relief)

7 A photon is E = hv h is Planck s constant ( J-sec) v is the frequency of the photon Frequency is equivalent to the quotient of the speed of light ( m/sec) divided by the wavelength High-energy radiations have a short wavelength and a high frequency The interaction of a photon beam with matter results in the attenuation of the beam Four major interactions occur: -Compton Scattering -Thompson Scattering -Photoelectric Absorption - Pair Production RADIATION INTERACTIONS

8 RADIATION INTERACTIONS

9 RADIOBIOLOGY High energy particles collide into a living cell with enough energy they knock electrons free from molecules that make up the cell Most damage occurs when DNA(deoxyribonucleic acid) is injured. DNA contains all the instructions for producing new cells Ionizing radiation causes damage in two way: 1.Indirectly H2O in our bodies absorbs radiation, produces free radicals which react with and damage DNA strand 2.Directly radiation collides with DNA molecule, ionizing it and damaging it directly

10 Unless repair occurs, the cumulative breaks in the DNA strand will lead to cell death Factors affecting cells response to radiation: (4 R s) Reoxygenation Repopulation Repair Redistribution RADIOBIOLOGY

11 Oxygen stabilizes free radicals Hypoxic (low O2 content) cells require more radiation to kill Hypoxic tumor areas REOXYGENATION Temporary vessel constriction from mass Outgrow blood supply, capillary collapse Tumor shrinkage decreases hypoxic areas Reinforces fractionated dosing

12 REPOPULATION Rapidly proliferating tumors regenerate faster e.g.. mucosa cells Determines length and timing of therapy course Regeneration (tumor) vs. Recuperation (normal) Reason for accelerated treatment schedules

13 REPAIR Sub lethal injury cells exposed to sparse ionization fields, can be repaired Cell death requires greater total dose when given in several fractions Most tissue repair in 3 hours, up to 24 hours Allows repair of injured normal tissue, potential therapeutic advantage over tumor cells

14 REDISTRIBUTION CELL CYCLE Cell cycle position sensitive cells S phase radio resistant G 2 phase delay = increased radio resistance Fractionated XRT redistributes cells Rapid cycling cells more sensitive (mucosa, skin) Slow cyclers (connective tissue, brain) spared

15 RADIOTHERAPY TREATMENT MODALITIES Teletherapy: use of sealed radiation sources at an extended distance i.e. x-rays, electrons (ionized particles), beta or gamma radiation Brachytherapy: use of small sealed radiation sources over a short distance ie.caesium or iridium Internal Isotope Treatment: administration of radioactive isotope systemically (around body, via bloodstream) Particle Therapy: radiation treatment with Neutrons or Protons

16 TELETHERAPY External beam radiotherapy the most common form of treatment in clinical use Range of energies available: - Superficial Machines ( kv);1cm depth -Orthovoltage Machines ( kV), 3cm depth -Megavoltage Machines (4-20MV), deep seated tumours e.g. Linear Accelerator

17 TELETHERAPY Linear Accelerator is large stationary x-ray tube Contains microwave technology that accelerates electrons through a wave guide When electrons hit a heavy metal target, x-rays are produced Various collimator systems in the gantry (head of the machine) shape the beam on it way out Change collimator systems to the shape of the tumour volume

18 TELETHERAPY Patient lies on a moveable couch beneath the machine and lasers in the room used to align the patient into the correct position Gantry is able to move 360 degrees around the patient delivering beams of radiation from different angles Kilovoltage arms (Kv source + Image intensifier) on Varian Linac for Image Guided Radiotherapy: Verification of treatment e.g. IMRT

19 MULTI-LEAF COLLIMATORS 40 pairs of tungsten leaves mounted external to the treatment head Each leaf transmits 1% of the beam Additional attenuation achieved with back up collimators These together reduces beam transmission of 0.5% of the primary bean

20 A form on conformal RT where the intensity of the radiation field varies across the treatment field: achieved by varying the position of the leaves during treatment Require multiple non uniform beams to achieve desired plan 2 Methods: Step and Shoot or Dynamic 3D treatment requires online imaging Reliable Immobilisation IMRT

21 CONVENTIONAL RT VS. IMRT

22 BRACHYTHERAPY Brachytherapy is the use of sealed radioactive sources placed either on or within a site involved with a tumour. 3 Types: Mould Treatment- superficial tumours Intracavitary Treatment e.g.. Cervical treatment using Iridium-192/Caesium-137 Interstitial Treatment e.g. radioactive gold seeds/ grains for prostate cancer

23 BRACHYTHERAPY Radio isotope No. of Isotopes E of Gamma Rays Half-life Other Emissions Cost Physical State Stability of daughter product Specific Activity Cobalt60 Two Photons 1.17 MeV 1.33 MeV 5.27 years Beta Particles Relatively Cheap Flaky Solid Nickel- Stable High Iridium-192 Range to MeV 74 years Beta Particles Relatively cheap Solid Plantinumstable High Caesium Single Photon MeV 30 years Beta Particles Relatively Cheap Solid Bariumstable Moderate Radium- 226 Range MeV 1620 years Beta +Alpha particles High Putty-like solid Long line of radioactiv edaughter products. High

24 BRACHYTHERAPY Aferloading Machine Designed to reduce dose to staff Method whereby empty source containers are placed into a body tissue/cavity and the radioactive sources are loaded at a later time More time ensuring accurate position Radiograph /CT of inert sources Sources are delivered remotely with the patient in the theatre room and staff at console area Treatment complete, retracted Patient does not remain radioactive Short hospital visits/ outpatient appointments

25 BRACHYTHERAPY Very steep dose rates around source High dose rate to the tumour and adjacent tissue and low dose further out to normal tissue Fewer side effects

26 High LET i.e. higher biological damage along its track or highly focused deposit of radiation (Bragg Peak) Neutrons : Downside: not selective for cancer cells, therefore more damaging to normal tissue Severe late side effects EU + USA Protons: +highly localised, high peak in their beam, use of absorbing materials and manipulation of the beam= Similar action to x-rays PARTICLE THERAPY Useful for inaccessible tumours i.e. of the eye, pituitary, Limitation: cost and technology required Use EU, USA and 1 centre in Clatterbridge in UK

27 PROTON TREATMENT

28 PROTON RADIOTHERAPY Disadvantages Set up proton facility Cost(11/2 times more that LA) Training Problems with breakdown :1 accelerating structure Demands on immobilisation

29 SIDE EFFECTS OF RADIOTHERAPY Acute Effects: Those which occur early ( within the first few weeks to 3 months of treatment) Non-permanent/ Reversible Long term side effects are those that occur months after completion of a course of treatment Permanent/ Irreversible Most patients will experience a skin reaction and fatigue Side effects depend on the what area is being treated Management requires skills of Multi-disciplinary Team

30 SPECIAL TECHNIQUES Respiratory Gating Lung and Gastrointestinal tumours Track breathing and location of tumour Used with IMRT

31 Gamma Knife Radiosurgery Malignant and benign conditions of the brain Patient fitted with an aluminium head frame with approximately 200 apertures through which radioactive cobalt-60 sources are focused at the target Area to be treated mapped out using MRI,CT,PET and angiography High dose can be delivered to the exact shape of the tumour with highly focused radiation beams, accurate to 0.5mm SPECIAL TECHNIQUES

32 Total Body Irradiation Blood related cancers e.g. Leukaemia Part of a preparative regime for bone marrow transplant Used in conjunction with chemotherapy to destroy the patient s immune system and prevent rejection by the donor bone marrow cells Total body irradiation, shielding of lung to prevent lung damage Using a standard Linear Accelerator with extended distance to encompass entire patient in radiation field SPECIAL TECHNIQUES

33 Tomotherapy Combination of two technology systems: Spiral CT scanner and Intensity Modulated Radiotherapy Treatment delivered slice by slice therefore the entire volume can be treated at once (rather that multiple beams) Cone beam capacity to take CT image prior to treatment for treatment matching to exact location of tumour Typical prostate treatment takes 3-5 minutes vs Linac 6 centres in UK RADIOTHERAPY DEPARTMENT

34 NUCLEAR MEDICINE Nuclear Medicine is the clinical application of unsealed radiation source Diagnostic, Localisation, Treatment Radiopharmaceutical : pharmaceutical is chemical substance that will selectively seek out the tumour cells that you want to locate. A radionuclide is added that will not interfere with the uptake Administered in-vitro or in-vivo (ingestion, inhalation, intravenous) Diagnostic: a gamma camera will show up hot spots ( areas appear dark due to higher uptake of radiopharmaceutical, i.e.. With good blood supply or greater metabolic activity or appear as a cold spot=less activity

35 Half life is the time it takes for half the nuclei in an atom to decay Effective half life 1 / Teff =1/ Tphysical + 1/ Tbiological Tc 99M= T ½ =6 hours Short half life=scanning procedure data collected quickly low dose to patient Extracted by kidneys in Urine Unit of measurement in mci 1mCI=37MBq TECHNETIUM-99MM

36 BONE SCAN TC-99M

37 Treatment: Hyperthyroidism-Iodine-131 NUCLEAR MEDICINE Ablation therapy for carcinoma of the thyroid- Iodine- 131 Bone pain palliation- Stontium-89 Treatment for Polycythaemia Ruba Vera -32P Sodium phosphate Non-Hogkins Lymphoma- Radioactive Monoclonal Antibodies-

38 Disadvantages: Radiopharmaceuticals used in treatment have a longer half life Longer in-patient stays in isolation Radiation exposure to staff Minimal family visits Expensive NUCLEAR MEDICINE Long term effects -leukaemia

39 Physics continues to play a vital role in advancing radiotherapy Installation and commissioning of new equipment Maintenance and Quality Assurance checks of equipment safe and fit for purpose Dosimetry and planning MEDICAL PHYSICS Radiation Protection and safety Work closely with the oncologists and radiation therapists in designing, planning and executing accurate and safe delivery of radiation treatments for our patients